1. ### Measuring density with ultrasonics

I'm interested in determining the density of a dough. I want to be able to continuously measure the density of the dough as it rises. My thought was to use an ultrasonic wave and measure the time it takes to reflect through the dough I would assume that as the dough ferments and the amount of...
2. ### Acceleration a Function of Density, yet Density is Constant?

I have used the search feature and tried very hard to find a thread where someone has asked this question and received an answer that is at the [low] level of understanding that I have. I'm sorry if this question seems ignorant -- which it may be, because I am not a physics student -- but I am...
3. ### Gravity/density equation? Giant ball of water

Can you help me find the equation for determining density when also taking the object's own center of gravity into account? For example, say I have an Earth-sized volume of water (or pick any simple spherical object). You have to account for the increase of density as you go closer to the center...
4. ### Estimate stopping force of roof versus tornado

Problem statement In the not-so distant past, authorities recommended leaving the windows to a house open in a tornado to equalize the pressure and avoid blowing off the roof. We can estimate the validity of the advice. Assume the pressure inside the house is one atmosphere. Approximate...
5. ### Finding magnetic flux density from magnetization vector

Homework Statement A long cylinder of radius a with magnetization vector M=M_0*(r/a)^2*a_φ. Find the magnetic flux density inside and outside the cylinder. Homework Equations J_m=∇×M J_ms=M×a_n[/B] A=(μ_0/4*π)*(∫(J_m/R)dv+∫(J_ms/R)ds) B=∇×A The Attempt at a Solution Basicly what I thought...
6. ### Gauge pressure under water

Homework Statement Approximately how deep into water must a diver dive to reach the point where the gauge pressure is 1 atm. (1 atm = 1.013 x 10^5 N/m^2) (assume fresh water) Homework Equations gauge pressure = pgd density of fresh water p = 1 kg/m^3 The Attempt at a Solution pgd = (1...
7. ### Finding the pressure at a given height?

I am having trouble trying to derive the air pressure at a given height. So far, I have considered a 1m^2 patch of area, and the pressure is the weight of all of the air above this patch. So P= \int_R^{\infty}g(x)\rho(x)dx So P= GM\int_R^{\infty}\frac{1}{x^2}\rho(x)dx But then I don't know...
8. ### Aluminium covered with gold submerged into water

Homework Statement A piece of aluminum is completely covered with a gold shell to form an object of weight W. When you suspend the object from a spring balance and submerge it in water, the balance...
9. ### What is the density of light?

What is the density of light? I'm relatively new to Physics and very new to the forum, so please forgive any (potentially) hilarious mistakes or stupidity in my question, knowledge, and use of the thread. But really, what is the density of light? Light is a particle like anything else, and all...
10. ### Buoyant forces problem

Homework Statement A man decides to make some measurements on a bar of gold before buying it at a cut-rate price. He find that the bar weighs 2000 N in air and 1600 N when submerged in water. Is the bar gold? Homework Equations B = density* V* g The Attempt at a Solution I tried to use the...
11. ### Capacity of a Barge

Homework Statement An open barge has the dimensions shown in the figure. https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/59/59574-46462a33e8dd3e05fa12094d99749d9c.jpg [Broken] If the barge is made out of 5.2-cm-thick steel plate on each of its four sides and its bottom...
12. ### Droplet of ballpoint ink in water (why)

I was wondering, a ballpoint pen ink droplet is droped on water, it floats and moves, why? Is it density, viscosity, surface tension or something else. Im pretty stuck
13. ### Calculating energy density in the early Universe

Homework Statement I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Homework Equations The Attempt at a Solution Now, I've found an equation to calculate the energy...
14. ### Lighter than air frame

Can you use a vacuum, or lighter than air gas within a tubular frame network to neutralize the apparent weight of the frame? If this is possible what is thee smallest possible size you could make this frame, I understand that the more you scale it up the lighter proportionately the frame would...
15. ### Density, buoyancy, and volume in static fluids

Homework Statement A rock is suspended by a light string. When the rock is in air, the tension in the string is 35.7N . When the rock is totally immersed in water, the tension is 25.9N . When the rock is totally immersed in an unknown liquid, the tension is 19.6N . Homework Equations Density =...
16. ### Proof of disk moment of inertia using area density

Homework Statement Disk with radius R σ = M/A I = ∫ mr2 Homework Equations Today we learned how to derive various moments of inertia via density equations (M/L, M/A, M/V). I understand all of them except on how to get MR2/2 for a disk. The Attempt at a Solution I = ∫mr2 σ = M/A dM =...
17. ### Is magnetic flux constant?

I know that the equation for magnetic flux is \Phi=\int \vec{B} \cdot dA. It seems to me that this is like integrating the density function a rod with respect to x, which simply gives you the mass which is constant. I was wondering whether the same thing applies here: is magnetic flux a constant?
18. ### Density at the centre of the sun

Hello, here is the question I have to answer; I am aware that the gravitational energy of one layer of thickness dr is dU=-\frac{GM(r)dm}{r} and that ultimately I will have to integrate this over all radii but I am unclear about the expression for \rho_{center}. The only thing that springs to...
19. ### Two Balls Drop, what happens to the distance?

Homework Statement Ball A is dropped from the top of a building. One second later, ball B is dropped from the same building. As time progresses, the distance between them A) increases. [<-- Correct Answer] B) remains constant. C) decreases. D) cannot be determined from the information given...